Modified organopolysiloxanes have been prepared heretofore by reacting monomers containing aliphatic unsaturation with organopolysiloxanes containing terminal hydroxyl or hydrolyzable groups in the presence of free radicals as shown in U.S. Pat. Nos. 3,555,109 and 3,776,875 to Getson. Also U.S. Pat. No. 3,631,087 to Lewis describes a process for preparing modified organopolysiloxanes by gradually adding a mixture of monomers and free radical initiators to preheated organopolysiloxanes. U.S. Pat. No. 3,694,478 to Adams et al discloses a process for preparing modified organopolysiloxanes by the gradual addition of free radical initiators to a preheated mixture containing an organopolysiloxane and an organic monomer having aliphatic unsaturation. U.S. Pat. No. 4,032,499 to Kreuzer et al describes a process for preparing modified organopolysiloxanes by reacting monomers containing aliphatic unsaturation with organopolysiloxanes containing hydrolyzable or hydroxyl groups in the presence of free radical initiators and an inert liquid having a boiling point up to about 100.degree. C. at 760 mm Hg (abs.), in which the inert liquid is a nonsolvent for the organopolysiloxanes and the resultant reaction product at the polymerization temperature. Polyolefin filled vinylorganopolysiloxane compositions which are prepared by polymerizing monomers having aliphatic unsaturation in the presence of vinylorganopolysiloxanes and free radical initiators are described in U.S. Pat. No. 4,014,851 to Bluestein.
Although organopolysiloxane elastomers have been used in various industrial applications because of their thermal stability, dielectric properties and resistance to atmospheric deterioration, it has been found that in certain applications there organopolysiloxane elastomers do not have the desired properties. Attempts to improve the physical properties by adding reinforcing fillers or agents, such as polytetrafluoroethylene fibers, have not improved the physical properties to the desired degree. For example, when polytetrafluoroethylene fibers have been dispersed in a random manner in an organopolysiloxane, it was found that it was difficult to form a homogeneous mixture. Also, it has been found that the modified organopolysiloxanes prepared heretofore have a tendency to shrink during curing. This property is especially undesirable when the composition is used as a molding or potting composition.
Therefore, it is an object of this invention to provide organopolysiloxane compositions containing in situ generated particulate matter. Another object of this invention is to provide a method for preparing modified organopolysiloxanes containing in situ generated particulate matter. Still another object of this invention is to prepare modified organopolysiloxanes by reacting SiH containing organopolysiloxanes with monomers containing aliphatic unsaturation in the presence of free radical initiators. A further object of this invention is to provide curable organopolysiloxanes containing in situ generated particulate matter. A still further object of this invention is to provide elastomeric compositions having improved physical properties.